This invention relates to laboratory testing procedures and, more particularly, to apparatus for preparing liquid samples of urine and the like for examination.
In the field of clinical testing, it is often important to isolate and accurately sample a specific volume of fluid. As an example, one type of routine medical test is an analysis of a patient's urine to determine the amounts of sugar, albumin, and solids present in the specimen. As part of this analytical procedure, microscopic studies are performed to determine the presence and amount of cellular elements such as erythrocytes, leukocytes, epithelial cells, casts, and crystals in the urine. In a standard procedure for making such determinations, a precise volume of urine is centrifuged to preferentially redistribute the cellular elements in the lower portion of a container tube, and then liquid from the lower portion is transferred to a slide for observation.
In obtaining samples for microscopic observation, it is important that the nature of the sample finally placed onto the the microscopic slide not be dependent upon the individual technique of the person who prepares the samples. To this end, an approach and apparatus was developed for isolating a precise volume of liquid at the bottom of a tube initially having a larger volume of liquid, with a pipette having a diametrically enlarged chamber that seals against the inner wall of the container so as to isolate the sample. After the seal is formed, the portion of liquid above the seal is decanted by inverting the tube and pipette with the seal intact. The tube and pipette are righted, and then after mixing the sample, a portion is drawn into the chamber for transferring to the slide. This technique has proved highly successful and popular in standardizing the microscopic urine testing procedure.
The above-described testing procedure has several drawbacks, however, particularly when used for large-scale laboratory testing wherein many samples are to be studied. Since the pipette is hollow and initially filled with air, it tends to float upwardly when placed into the liquid-filled tube, thereby breaking the seal between the outer portion of the chamber and the wall of the tube and allowing liquid circulation between the liquids being isolated from each other. Consequently, it is sometimes necessary to hold the pipette in place manually. Further, when the tube and pipette are inverted to decant the portion of the liquid to be removed, the pipette must be held in place manually to maintain the seal and thereby retain the small sample. With this constraint, it is impossible to decant multiple containers at one time, as for example by placing a large number of containers with inserted tubes into a rack and then partially inverting the rack to decant all of the containers at once. Finally, because the pipette must be held in place manually when decanting, it is possible that the hand may be splashed with a portion of the liquid being decanted, which is undesirable both hygenically and because of cross contamination of samples.
There therefore exists a need for apparatus which allows the standardized preparation of a urine sample for microscopic observation, but also provides for the positive retention of the seal between the tube and the container wall during sampling. Further, such apparatus should be economical to manufacture and should allow rapid processing of samples in large numbers with minimal variation of the technique now well established in laboratories worldwide. The present invention fulfills this need, and further provides related advantages.